Amplifier feed system



Sent. 26, 1933. B Dow Er AL 1,927,926

AMPLIFIER FEED SYSTEM Filed Nov. 19, 1950 l I 'm INVENTORS l fm gmfwvmgo @JJ/90W, A J. Samira/wy 40 leads.

Patented Sept. 26, 1933 UNITED STATES AMPLIFIER FEED SYSTEM Jennings B. Dow, Alexandria, Va., and Harry Novotney, Bremerton, Wash.

Application November 19, 1939 serial No. 496,778

5 claims. (o1. 25o-iv) (Granted under the Act of March 3, 1883,.as amended April 30, 1928; 370 0. G. 757)l Our invention relates broadliy Ito high frequency amplifiers and more particularly to a system for progressively feeding electron tube stages for the eflicient amplification of radio frequency energy.

One of the objects of our invention is to provide means for successively feeding high frequency signaling energy from one electron tube amplifier to another in a high frequency transmission system.

Another object of our invention is to provide an arrangement of feed lines interconnecting the successive electron tube stages of a high frequency transmitter for increasing the excitation of such stages.

A further object of our invention is to providea circuit arrangement for a high frequency transmitter having feed lines interconnecting the several electron tube stages of a transmitter with means for adjusting the interconnecting circuits to resonant at a predetermined frequency.

Other and further objects of our invention reside in an efficient form of high frequency feed system as more fully set forth in the specification hereinafter following by reference to the accompanying drawing which diagrammatically illustrates the principles of our invention.

In certain amplifiers and particularly high frequency amplifiers, it is difficult to obtain ade-q quate excitation voltages on the grids of the tubes owing to the highreactance offered by the lengths of the leads to the grids, and the low reactance which exists across the input. This is particularly the case when tubes are used` as amplifiers at very high frequencies. In the system of our invention the inductance of the grid leads is actually used to advantage as a part of a tuned circuit comprising that inductance plus inductance intentionally added by extending the 'grid Means are also provided for adjusting the tuned grid circuit so formed as well as the tuned plate circuit preceding it. By use ofthe circuit arrangement of our invention, greater excitation voltages may be obtained on the grids of the driven tubes than with excitation methods heretofore known, thereby obtaining a considerable increase in eiciency of the operating characteristics of the transmitter. The center points of the adjusting elements provide convenient low alternating potential points at which to connect grid bias potential sources for the different electron tube stages in the transmitter. The use of the adjusting elements increases the electrical rigidity of the system in that alternating potentials which do not produce potential nodes at the centers of the adjusting elements in ytuning the circuits in "r and arranged to excite the grids of the power f amplifier tubes 3 and 4 through the interposition of the adjusting element 6 and conductors 13,15, 14 and 16 which constitute asymmetrical feed line. These conductorsmaybe straight as is shown by 17, 19, 18, and 20 in the second inter coupling system, or may be coiled in the form of small diameter solenoids asindicated in the first intercoupling system where it may beA convenient to restrict physical separation between stages of the amplifier system. The operation of tuning the arrangement consists in moving the contacts 6a and 6b lof adjusting element 6 along the line until the circuit consisting of that part of the line represented by 15, 16 and the intraelectrode capacities lof the second stage, together with the neutralizing capacities 10 of that stage, is tuned to resonate at the exciting frequency, afterwhich the final adjustment of the tuned plate circuit of the preceding stage consistingof the plate circuit tuning condenser 12 and that circuits and line 17, 19, 18 and'20 between the next stage which is constituted by tubes 30 and 31. f

The tubes 30 and 31 constituting the third group of tubes in the transmitter and comprising the second power amplification stage are also connected in balanced relationship in a manner similar to the balanced relationship of the first power amplifier stage including tubes 3'and 4 and similar to the balanced relationship of the mastervoscillator constituted by tubes l and v2.A The adjusting element 7 is adjustable along the lines 17-19 and 18-20, amid tap connection being taken through resistance 32 to Vground 33. This mid-tap connection is similar to the midtap connection provided to inductance 6 through resistance 34 to ground 33. The output Acircuit isturned by means of condenser 35. The s'ucceeding stage of power amplification has been represented by tubes 36 and 37 connected in balanced relationship, the inputcircuits of `the tubes being coupled to the output circuits of tubes 39 and 31 through feed lines constituted by conductors 21, 22, 23, 24, 25 and 26.

In the case of a line between two stages operating at very high frequencies, it may not be practicable even with the closest possible physical separation between stages and straight conductors to obtain a line short enough to employ a single adjusting element, in which case two-are employed as shown by 8 and 9. In thisy case, that portion of the line represented by the-'conductors 23 and 24 remains untuned. A mid-point in the adjusting element 9 connects through resistance 29 to ground 33. The output circuit is tuned by means of condenser 38. The output of the last stage of power amplification constituted by tubes 36 and 37 is connected to the primary winding 39 of coupling system 40, the primary winding 39 being tuned by means of condenser 41. The secondary winding 42 of the coupling system 40 connects through condensers 43 and 44 with the radiating system, whichin this instance we have illustrated as comprising a doublet 45. Each stage of amplification is separately adjusted .to compensate `for capacity effects by neutralizing capacities such as are shown at 46 and 47 for the amplifier tubes 30 andl, and by the neutralizing capacities 48 and 49 as shown connected with the circuits of power amplifier tubes 36 and 37. The plate circuits for all of the tubes are energized from the common source 50 through radio frequency choke coils 27. The cathodes of all of j through transformer 52 to the busses 53 which A extend to the cathode circuits of each of the tubes. The oscillator constituted by tubes 1 and 2 includes a resonant circuit containing inductance 54 and adjustable capacityv55 with a tap connectionextending from inductance 54 through resistance 56 to ground 33 as shown. The several tap connections extending from ground connection 33 enable the required operating potential to be applied to the several grids of' the electron tubes. Blocking condensers 28 are arranged in the plate circuits of each of the tubes. Filament by-pass condensers 57 are arranged in each of the cathode circuits forV equalizing the effect of the supply upon the tube circuits from the source 51. rI he transmitter is adjusted by shifting the adjusting element 6 alongfthe inductances disposed in opposite sides ofthe feed line and by shifting the adjusting element '7 along busses 17A-19 and Vl8--20 and also by shifting adjusting elements 8 and 9 along busses 20-23-25 and 22-24-26. The position of the several adjusting elements is finally selectedwhere the several output oircuits resonate at apredetermined frequency which may be accurately adjusted by shifting tuning condensers 12, 35, 38 and 41. By virtue of this novel arrangement of the successive amplification stages, we transfer a maximum amount of energy from the output circuit of one amplifier stage to K the input circuit of the succeeding amplifier stage. The effective inductance in each intercoupling circuit is very accurately selected by shifting the adjusting elements to desired position. In this way, the advantages hereinbefore set forth are obtained. `That is, greater excitation voltage may be delivered to the grids of one amplification system from a preceding amplification system than is practical in other forms of high frequency coupling circuits.

The resistors 56, 34, 32 and 29 serve to estab- Y lish a'p'ath to the grid electrodes of the differentkgroups of electron tubes by which a pre- Ytion with the adjustable condensers 12, 35 and 38 tothe desired operating frequency. The adjustmen1L of 'the several condensers and the' position of the several adjusting elements after being made, may be made fixed for the operation of the transmitteron a predetermined frequency. l The coupling system of our invention is particularly adapted in short wave transmitters employing four element tubes adapted to operate above 40,00 kilocycles.` While we have described the circuit arrangement of our invention in one of its preferred embodiments, we desire-that it be understood that modifications may be made and that no limitations -upon our invention, are intended other than are imposed by the scope of the appended claims.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposeswithout the payment of any royalties thereon. F

What we claim as new and desire to secure by Letters Patent of the United States is as follows:

l. In a high frequency amplifier, a multiplicity of electron tube stages, conductors connecting the output circuit of one stage with the input circuit of the succeeding stage, a radiating circuit connected with the output circuit of the last electron tube amplification stage, and means slidable along said conductors for selectively emresonating those capacities associated rwith the input to said succeeding stage.

2. In a high frequency amplifier, a multiplicity of electron tube stages, conductors connecting the output circuit of-one stage with the input; .circuit of the succeeding stage, a radiatingv circuit connected withv the output circuit of the last v,electron tube amplification stage, and means displaceable longitudinally of said, conductors for selectively employing the inductance of said conductors for adjustably resonating those capacities associated with the input to said succeeding stage. f. v

3. In a high frequency amplifier, a multiplicity of electron tube stages, conductors connecting the output circuitA of one stage with the input circuit of the succeeding stage, --a radiating'cir- ,cuit connected lwith the output circuit of the last electron tube amplification stage, and bridging members shunting said conductors and shiftable along said conductors for adjusting the frequency. of the interstage coupling circuits between said electron tube amplification stages.

4. In a high frequency transmission system,- a Amultiplicity of groups of electron tube stages, a pair of conductors interconnecting the output circuit of one group with' a succeedinggroup constituting said electron-tube amplifier stages, said conductors each including inherent inductance, variable capacity means connected in shunt with said conductors, and a bridging contactor shiftable longitudinally along said conductors for including selected amountsA of the Vinherent inductance of said conductors in circuit with said variable capacity means and adjusting-the interfos 'ployingthe inductance of saidv conductors forc5 ing selected amounts of the inherent inductance of said conductors in circuit with said variable capacity means and adjusting the intercoupling circuits between said groups of electron tubes to a predetermined frequency, and means connected to a. mid-point on said bridging contactors for applying potential to the grids of each of said group of electron tubes.

JENNINGS B; DOW. HARRY J. NOVOTNEY. 

